/* 
  THIS CODE AND INFORMATION IS PROVIDED "AS IS" WITHOUT WARRANTY OF 
  ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT LIMITED TO 
  THE IMPLIED WARRANTIES OF MERCHANTABILITY AND/OR FITNESS FOR A 
  PARTICULAR PURPOSE. 
  
    This is sample code and is freely distributable. 
*/ 
using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.Runtime.InteropServices;

using System.Security;
using System.Security.Permissions;

namespace Anolis.Core.Utility.Quantization {
	
	public unsafe abstract class Quantizer {
		
		/// <summary>Construct the quantizer</summary>
		/// <param name="singlePass">If true, the quantization only needs to loop through the source pixels once</param>
		/// <remarks>If you construct this class with a true value for singlePass, then the code will, when quantizing your image,
		/// only call the 'QuantizeImage' function. If two passes are required, the code will call 'InitialQuantizeImage'
		/// and then 'QuantizeImage'.</remarks>
		protected Quantizer(bool singlePass) {
			_singlePass = singlePass;
		}
		
		/// <summary>Quantize an image and return the resulting output bitmap</summary>
		/// <param name="source">The image to quantize</param>
		/// <returns>A quantized version of the image</returns>
		[SecurityPermission(SecurityAction.LinkDemand, Flags=SecurityPermissionFlag.UnmanagedCode)]
		public Bitmap Quantize(Image source) {
			
			// Get the size of the source image
			int	height = source.Height;
			int width = source.Width;
			
			// And construct a rectangle from these dimensions
			Rectangle	bounds = new Rectangle(0, 0, width, height);
			
			// First off take a 32bpp copy of the image
			Bitmap	copy = new Bitmap(width, height, PixelFormat.Format32bppArgb);
			
			// And construct an 8bpp version
			Bitmap	output = new Bitmap(width, height, PixelFormat.Format8bppIndexed);
			
			// Now lock the bitmap into memory
			using(Graphics g = Graphics.FromImage(copy)) {
				g.PageUnit = GraphicsUnit.Pixel;
				
				// Draw the source image onto the copy bitmap,
				// which will effect a widening as appropriate.
				g.DrawImageUnscaled(source, bounds);
			}
			
			// Define a pointer to the bitmap data
			BitmapData	sourceData = null;
			
			try {
				// Get the source image bits and lock into memory
				sourceData = copy.LockBits(bounds, ImageLockMode.ReadOnly, PixelFormat.Format32bppArgb);
				
				// Call the FirstPass function if not a single pass algorithm.
				// For something like an octree quantizer, this will run through
				// all image pixels, build a data structure, and create a palette.
				if(!_singlePass)
					FirstPass(sourceData, width, height);
					
				// Then set the color palette on the output bitmap. I'm passing in the current palette 
				// as there's no way to construct a new, empty palette.
				output.Palette = this.GetPalette(output.Palette);
			
				// Then call the second pass which actually does the conversion
				SecondPass(sourceData, output, width, height, bounds);
			} finally {
				// Ensure that the bits are unlocked
				copy.UnlockBits(sourceData);
			}
			
			// Last but not least, return the output bitmap
			return output;
		}
		
		/// <summary>Execute the first pass through the pixels in the image</summary>
		/// <param name="sourceData">The source data</param>
		/// <param name="width">The width in pixels of the image</param>
		/// <param name="height">The height in pixels of the image</param>
		protected virtual void FirstPass(BitmapData sourceData, int width, int height) {
			
			// Define the source data pointers. The source row is a byte to
			// keep addition of the stride value easier (as this is in bytes)
			byte*	pSourceRow = (byte*)sourceData.Scan0.ToPointer();
			Int32*	pSourcePixel;
			
			// Loop through each row
			for(int row = 0;row < height;row++) {
				// Set the source pixel to the first pixel in this row
				pSourcePixel = (Int32*)pSourceRow;
				
				// And loop through each column
				for(int col = 0;col < width;col++, pSourcePixel++)
					// Now I have the pixel, call the FirstPassQuantize function...
					InitialQuantizePixel((Color32*)pSourcePixel);
					
				// Add the stride to the source row
				pSourceRow += sourceData.Stride;
			}
		}
		
		/// <summary>Execute a second pass through the bitmap</summary>
		/// <param name="sourceData">The source bitmap, locked into memory</param>
		/// <param name="output">The output bitmap</param>
		/// <param name="width">The width in pixels of the image</param>
		/// <param name="height">The height in pixels of the image</param>
		/// <param name="bounds">The bounding rectangle</param>
		[SecurityPermission(SecurityAction.LinkDemand, Flags=SecurityPermissionFlag.UnmanagedCode)]
		protected virtual void SecondPass(BitmapData sourceData, Bitmap output, int width, int height, Rectangle bounds) {
			
			BitmapData	outputData = null;
			
			try {
				// Lock the output bitmap into memory
				outputData = output.LockBits(bounds, ImageLockMode.WriteOnly, PixelFormat.Format8bppIndexed);
				
				// Define the source data pointers. The source row is a byte to
				// keep addition of the stride value easier (as this is in bytes)
				byte*	pSourceRow = (byte*)sourceData.Scan0.ToPointer();
				Int32*	pSourcePixel = (Int32*)pSourceRow;
				Int32*	pPreviousPixel = pSourcePixel;
				
				// Now define the destination data pointers
				byte*	pDestinationRow = (byte*)outputData.Scan0.ToPointer();
				byte*	pDestinationPixel = pDestinationRow;
				
				// And convert the first pixel, so that I have values going into the loop
				byte	pixelValue = QuantizePixel((Color32*)pSourcePixel);
				
				// Assign the value of the first pixel
				*pDestinationPixel = pixelValue;
				
				// Loop through each row
				for(int row = 0;row < height;row++) {
					// Set the source pixel to the first pixel in this row
					pSourcePixel = (Int32*)pSourceRow;
					
					// And set the destination pixel pointer to the first pixel in the row
					pDestinationPixel = pDestinationRow;
					
					// Loop through each pixel on this scan line
					for(int col = 0;col < width;col++, pSourcePixel++, pDestinationPixel++) {
						// Check if this is the same as the last pixel. If so use that value
						// rather than calculating it again. This is an inexpensive optimisation.
						if(*pPreviousPixel != *pSourcePixel) {
							// Quantize the pixel
							pixelValue = QuantizePixel((Color32*)pSourcePixel);
							
							// And setup the previous pointer
							pPreviousPixel = pSourcePixel;
						}
						
						// And set the pixel in the output
						*pDestinationPixel = pixelValue;
					}
					
					// Add the stride to the source row
					pSourceRow += sourceData.Stride;
					
					// And to the destination row
					pDestinationRow += outputData.Stride;
				}
			} finally {
				// Ensure that I unlock the output bits
				output.UnlockBits(outputData);
			}
		}
		
		/// <summary>Override this to process the pixel in the first pass of the algorithm</summary>
		/// <param name="pixel">The pixel to quantize</param>
		/// <remarks>This function need only be overridden if your quantize algorithm needs two passes, such as an Octree quantizer.</remarks>
		protected virtual void InitialQuantizePixel(Color32* pixel) {
		}
		
		/// <summary>Override this to process the pixel in the second pass of the algorithm</summary>
		/// <param name="pixel">The pixel to quantize</param>
		/// <returns>The quantized value</returns>
		protected abstract byte QuantizePixel(Color32* pixel);
		
		/// <summary>Retrieve the palette for the quantized image</summary>
		/// <param name="original">Any old palette, this is overrwritten</param>
		/// <returns>The new color palette</returns>
		protected abstract ColorPalette GetPalette(ColorPalette palette);
		
		/// <summary>Flag used to indicate whether a single pass or two passes are needed for quantization.</summary>
		private bool	_singlePass;
		
	}
}
